Field of the Invention
The present invention relates to a stable solution of a ring-opened polymer. Specifically, the present invention relates to a stable solution which is obtained from the ring-opening reaction of an N,O-heterocyclic compound and a DOPO-based compound. The stable solution is useful for the preparation of a laminate.
Descriptions of the Related Art
Printed circuit boards are circuit substrates that are used for electronic devices to load other electronic components and to electrically connect the components to provide a stable circuit working environment. One kind of conventional printed circuit board is a copper clad laminate (CCL), which is primarily composed of resin(s), reinforcing material(s), and copper foil(s). Conventional resins include epoxy resins, novolac resins, polyamine formaldehydes, silicones and Teflon®; and conventional reinforcing materials include glass fiber cloths, glass fiber mats, insulating papers and linen cloths.
Generally, a printed circuit broad can be prepared as follows: immersing a reinforcing material such as a glass fiber fabric into a resin; curing the immersed glass fiber fabric to a half-hardened state, i.e. B-stage, to obtain a prepreg; superimposing certain layers of the prepregs and superimposing a metal foil on at least one external surface of the superimposed prepregs to provide a superimposed object; hot-pressing the superimposed object, i.e. C-stage, to obtain a metal clad laminate; etching the metal foil on the surface of the metal clad laminate to form a defined circuit pattern; and finally, digging a plurality of holes on the metal clad laminate and plating these holes with a conductive material to form via holes to accomplish the preparation of the printed circuit broad.
In consideration of the subsequent electronic processes, a printed circuit board substrate must be provided with a certain thermal resistance, size stability, chemical stability, processability, toughness, mechanical strength etc. Generally, epoxy resin is the most popular resin in the printed circuit board industry since the printed circuit broad prepared with the use of epoxy resin can properly meet the above requirements. Epoxy resin, a reactive monomer, is a general name for organic polymer compounds with two or more epoxy groups in the molecular structure. A highly cross-linked net structure can be obtained by polymerizing molecules with high epoxy group content. Although such a highly cross-linked net structure possesses a relatively high hardness and glass transition temperature (Tg) as well as good chemical resistance, it is fragile and possesses poor impact resistance and both are disadvantageous to the subsequent process.
In view of the above, N,O-heterocyclic compounds with a
structure are now commonly used in substitution for epoxy resin or as a hardener to regulate epoxy resin. Due to a high proportion of benzene rings and C—N bonds in the structure, the N,O-heterocyclic compounds possess excellent thermal properties (such as thermal resistance, glass transition temperature and flammability), chemical properties and mechanical properties. In addition, the polymer prepared from a ring-opening polymerization of N,O-heterocyclic compounds has a large number of hydroxyl groups in its structure and a novolac laminate can be provided by the cross-linking reaction of the polymer itself. The use of the polymer in combination with an epoxy resin may enhance the thermal properties and mechanical properties of a final product and lower the contractility of the product so as to provide a high level laminate.
However, the flammability of the laminate prepared provided by the cross-linking reaction of the N,O-heterocyclic compound is insufficient, and thus, a phosphorus-containing flame retardant such as DOPO is usually applied to enhance the flammability of the prepared laminate. TW 1285653 discloses a phosphorus-containing cured benzoxazine resin, wherein an N,O-heterocyclic compound is mixed with DOPO-based compound powder and the resultant mixture is cured under high temperature and pressure to produce a substrate with improved flammability. However, the method is energy-consuming and incapable of controlling the reaction uniformity well.
The present invention provides a stable solution of a ring-opened polymer, which is a solution comprising a polymer of an N,O-heterocyclic compound and a DOPO-based compound.